I have a question about tile over radiant.

I have staple-up radiant with omega-type thin heat transfer plates. The subfloor is 3/4" Advantech.

I'm currently in the process of laying down 1/4" Hardibacker EZGrid over the Advantech using Versabond Fortified Thin-Set Mortar.

http://www.custombuildingproducts.com/ProductCatalog/SettingMaterials/LatexPortlandCementMortars/VersaBondFortifiedThinSet.aspx?user=arc&lang=en


We are screwing the hardibacker every 4" with 3/4" screws (to prevent penetration). We tried 1" screws but the tips still came through so we could not risk it.

My questions are as follows:
1. Am I using the correct type of thinset? The Hardibacker website says to use a latex or acrylic modified thinset. Does Versabond fall in this category?
2. Do I need a waterproofing / crack (anti-fracture) membrane over the hardibacker?
3. Is there anything I should be doing differently?

I have got mixed answers from tile companies. I talked to one today who said that because I have radiant under Advantech, I should have used a crack membrane such as Schluter Ditra instead of the hardibacker. He said that since I have already started with hardibacker, that I will need to use a waterproofing / anti-fracture membrane over the hardibacker. Otherwise, he said, my tile installation would only last for a couple years before breaking free. Others have not necessarily agreed with this.

I want an installation that lasts. What should I do?

Backerboard seems to be the rule on all the jobs I've been on,can't remember when the last time I saw someone use a crack membrane.Haven't seen or heard of any cracked tile issues.

Schluter Ditra is installed to uncouple the tile from the wood. If the wood is of sufficient thickness backer board may be eliminated with only the use of Ditra. I have just done this in my own home - works great. Before Ditra was widely used in this area, some installers used the isolation membrane to protect themselves from future problems. Once it is down - you know the rest of the story.

Good luck

[This message has been edited by plumbob (edited 03-04-2005).]